This invention relates generally to atomizer pump constructions for small hand-held dispensers and the like, and more particularly to pumps of the type having a hollow or ducted plunger which slidably carries a hollow piston and wherein the piston is movable on the plunger between high and low positions at the times of plunger movement. U.S. Pat. No. 3,724,726 dated Apr. 3, 1973 and issued to Susuki illustrates a pump of this type.
One of the problems associated with such pumps is that leakage of liquid from the pump cylinder tends to occur, especially past the area between the cylindrical walls of the plunger and the walls of the piston bore. In the Susuki construction, the fit between the plunger and piston bore has to be sufficiently loose to enable limited sliding movement to occur between the two parts, since during initial discharge the plunger moves first to expose or uncover the side orifices adjacent the lower part of the plunger. With a sliding fit of the type indicated, there is usually a limited amount of seepage through the bore of the piston, even during non-discharge of the dispenser in the case that it is lying either on its side or upside down.
One approach to the problem, that embraced by the Susuki device, was to establish a large surface contact between the plunger and piston, to maximize the length of the path that liquid would have to travel in order to leak out. While this arrangement partially reduced leakage, problems still existed. In insuring reliable operation, such a construction is seen to rely a great deal on a proper sliding fit between the piston bore and plunger. This involves critical tolerances which are usually difficult to achieve and adhere to, especially in mass production and where plastic components are involved. Accordingly, the critical tolerances which were involved resulted in unnecessarily high fabrication and assembly costs, which in some cases made the product prohibitively expensive.